fix(striker-ui): add button to upload files

striker-ui/components/Files/Files.tsx

@@ -1,11 +1,31 @@
+import { Box, IconButton } from '@material-ui/core';
+import AddIcon from '@material-ui/icons/Add';
+import { makeStyles } from '@material-ui/styles';
+
+import ICON_BUTTON_STYLE from '../../lib/consts/ICON_BUTTON_STYLE';
 import { Panel } from '../Panels';
 import Spinner from '../Spinner';
 import { HeaderText } from '../Text';
 
+const useStyles = makeStyles(() => ({
+  addFileButton: ICON_BUTTON_STYLE,
+}));
+
 const Files = (): JSX.Element => {
+  const classes = useStyles();
+
   return (
     <Panel>
+      <Box display="flex">
+        <Box flexGrow={1}>
           <HeaderText text="Files" />
+        </Box>
+        <Box>
+          <IconButton className={classes.addFileButton}>
+            <AddIcon />
+          </IconButton>
+        </Box>
+      </Box>
       <Spinner />
     </Panel>
   );

striker-ui/lib/consts/ICON_BUTTON_STYLE.ts

@@ -0,0 +1,12 @@
+import { BLACK, GREY, TEXT } from './DEFAULT_THEME';
+
+const ICON_BUTTON_STYLE: Readonly<Record<string, unknown>> = {
+  borderRadius: 8,
+  backgroundColor: GREY,
+  '&:hover': {
+    backgroundColor: TEXT,
+  },
+  color: BLACK,
+};
+
+export default ICON_BUTTON_STYLE;